Train dispatching system for railroads



Oct. 29, 1935. N. D. PRESTON El AL TRAIN DISPATCHING SYSTEM FOR RAILROADS Original Filed April 29, 1927 INVENTOR5 N.D. Presto/22nd H.D|'cke BY M THEIR ATTORNEY Patented Oct. 29, 1935 UNITED STATES PATENT since TRAIN DISPATCHING SYSTEM FOR RAILROADS Neil D. Preston and Oscar H. Dicke, Rochester, N. Y., assignors to General Railway Signal Company, Rochester, N. Y.

18 Claims.

This invention relates to a system of train dispatching by wayside signal indications, and more particularly to such a system wherein spring switches are employed at the passing sidings. This application is a division of our prior copending application Ser. No. 187,490 filed April 29, 1927.

Although the present invention is applicable to double track railroads, it is deemd expedient to show it applied to a single track railroad wherein traffic moves in both directions; and for this reason the invention has been shown applied to a single track railroad employing wayside signals of the absolute-permissive-block type.

In employing spring switches, namely switches which are held in a certain position by spring pressure but which may be trailed to the opposite position by the wheel flanges, to a single track railway system it is important to assure that the points are in the spring pressed position when a train moves in a direction against the points of the spring switch, and further if the points are at times locked it is important to assure that the points are not locked when a train moves in the trailing direction through the switch.

In view of the foregoing and other important considerations, it is proposed to employ spring switches wherein the switch points are held in one extreme position by a spring, and to employ a slow releasing means whereby if the switch points are trailed to the abnormal position against the action of such spring their return to the normal position will be appreciably retarded, so that, as a train trails through the spring switch the switch points will not be returned to the normal position between the passage of the successive trucks of the train, and these features have been shown and described in detail in our parent application.

It is further proposed to provide an electrically operated lock whichis controlled by a directional approach locking circuit, and to prevent the clearing of a signal in the face of an approaching train running toward the switch points if such approaching train has not locked the switch points in the normal position. Similarly, it is proposed to prevent clearing of a signal permitting movement of a train in a direction to trail the switch unless the electric lock mentioned is in its unlocked condition. Further, it is proposed to provide a switch stand for operating the switch points manually, and to provide a dual control selector whereby the switch points maybe mechanically connected to either the spring actuated switch operator or the switch stand. As a further feature of a railway system of the single track type employing spring switches, it is proposed to have both of the tracks of a passing siding offset from the main single track section to the same extent, so that trains passing in one direction diverge from their normal direction of traflic the same as do train-s moving in the opposite direction when passing through a passing siding, this is, however, not essential and the invention is not limited to such a track layout.

In dispatching the movement of trains over a single track railroad employing absolute-permis- 15 sive-block signals by wayside signal indications, it has heretofore been proposed to hold the starting and entering signals ateach end of each single track section at stop and provision was made for permitting clearing of one of these signals in response to manual control, provided traflic conditions are proper for the clearing of such signal. This has been proposed in the application of S. N. Wight, Ser. No. 120,423 filed July 3, 1926, and the present invention is an improvement on the system proposed in the application just mentioned.

It is of course recognized that the principal interference between movements of trains on a single track railway system resides principally in 30 the passage of trains moving in the opposite direction by each other, that is, trains making a, meet, but that there are instances where it is desirable to have a higher class or higher speed train pass another train, moving in the same direction, from the rear. In other words, the use of spring switches in a single track railway train dispatching system isextremely desirable as far as meets between trains is concerned, but that in spite of the rare necessity of a. train passing another train from the rear it is deemed expedient to make provision for one train overtaking another, and such provision has been made in the parent application.

Another feature of the present invention re- 45 sides in the provision of indicating means at the tower which not only indicates when a train is occupying the detector track circuit at the end of a passing siding, but also indicates the direction in which such train is moving, and resides 5 in the provision of means whereby the presence or absence of train on two different detector track circuits can be indicated at the same time over the same line circuit, and audible means for directing the train dispatchers attention to changes in these signals and indicating devices, and it is to these later features that the present invention is particularly directed.

Other objects, purposes and characteristic features of the invention will in part be apparent from the drawing and in part be pointed out hereinafter.

In describing the invention in detail reference will be made to the accompanying drawing in which the single figure shows the same system as shown in the parent application except that the two control relays of one single track section are controlled by the same line wire, and that the condition of occupancy of the detector track circuits at both ends of such single track section are indicated over the same linewire simultaneously.

Referring to the drawing it will be noted that the system disclosed is ratherinvolved, and for this reason the absolute-permissive-b1ock signal control features will be very briefly dealt with. In

the particular arrangement shown the absolutepermissive-block signal system is one employing opposite signals as distinguished from staggered signals, although either arrangement of signals may be used. In the arrangement shown the east bound signals have been successively numbered 2, 5 and 8, of which the signal 2 is the starting signal and the signal 8 is the entering signal. In a similar way, the west bound signals have been numbered I, 5, 3,, and I, of which the signal is the starting signal and the signal I is the entering signal. The signals I, 2, I, and 8 are stop-and-stay signals as conventionally shown by the square ended blades, as distinguished from permissive signals as conventionally indicated by pointed blades. Light signals may of course also be used if desired.

t will be noted that the various track relays have been numbered T with the proper numerical prefix corresponding to the signal immediately following such track relay, and that these track relays are normally energized by suitable track batteries which have for convenience been omitted. Also, it will be noted that the various home relays have been designated H with a prefix corresponding to the signals which they control.

It may be mentioned here that trains may follow each other through the single track section with proper signal protection in spite of the interdependence of the energizing circuits of the various home relays by reason of the provision of the usual directional stick relays, the function of which will not be described in detail but may be ascertained from the application of Wight heretofore mentioned. The circuits whereby the signals are controlled by their respective home relays have for convenience been omitted.

Superimposed manual c0ntroZ.As heretofore pointed out certain manual control is superimposed on the single track absolute-permissiveblock signal system which permits the dispatcher to hold certain trains so as to enable the making of train meets and passes from the rear in accordance with the wishes of the dispatcher and so asto facilitate train movement, as a whole. Although the dispatcher may supervise the control of trains over the entire system, only the mechanism at the dispatchers desk for the portion of the system shown in the drawing has been illustrated in the tower, which tower has been conventionally shown by the dotted square DT.

the single track section 0 in a manner more clearly pointed out when the operation of the system is considered. In order to indicate to the dispatcher the presence or a train on the detector track circuit at signal 2, or indicating the presence of such train on the detector track circuit adjacent the signal I, the line relays 21R and 11B have been provided. These line relays 21R and HR. in combination with the lever L govern the illumination of the indicating lamps 21W, 2IE, IIW and IIE.

It is desired to be understood that when considering the arrangement shown in the drawing that all of the apparatus and signal equipment shown in the parent application except certain of the control and indicating mechanism, should be assumed to be present in this divisional application as represented by the conventional illustration of the signals, spring switch mechanisms,

etc.

Referring to the drawing, the equipment in the tower DT includes the miniature track layout, the signal lamps 21W, 21E, 'IIW and HE; includes the lever L having contacts I50 and I5I, a battery I52 having its middle point connected to the common return wire C and two indicating relays of which one, namely relay 21R is responsive only to unidirectional or direct current and the other relay HR is only responsive to alternating current. The indicating relay 21R may be of any suitable construction rendering it responsive only to direct current, that is, may be :a device of the DArsonval type including a permanent magnet upon which the flux of a moving coil may act, or may be of any other suitable construction which renders it responsive to direct purrent only. This relay 21R has been conventionally shown as 'a relay includinga U -shaped iron yoke I53 having a winding thereon, and having the legs of this yoke provided with slugs or bucking coils I54, and having a soft iron movable armature I55. The bucking coils I54 are provided to avoid the fiow of alternating magnetism through legs of the yoke I53 and the attracting of the armature I55, so that this relay ZIR responds only to direct current.

The indication relay 'IIR, on the other hand is suitably constructed so as to respond only to alternating current, and in the particular arrangement shown this relay 11R has been shown connected to the secondary winding of a transformer I56, theprimary winding of which is connected directly in series with the direct current relay 21R and the line wire I51. This alternating currentline relay 'IIR can of course not be energized by direct current for obvious reasons, so that if there is direct current only flowing in the line wire I5! the indicating relay 'IIR will remain de-energized. Further, the indicating relay I'IR may be a relay of the alternating current induction type which in itself is of a construction so as not to render it responsive to direct current. In view of this fact the transformer I55 may be omitted if desired.

The control relays ZW and ZE may be of exactly the same construction as those described in the parent application; The system shown in the drawing includes certain filtering reactances and condensers, which condensers in many instances serve-as blocking condensers to prevent the flow of direct current, and since these reactances and condensers need no specific, description, it is believed expedient to now take up the operation of the control and indication part of the system.

Operation of system.Let us assume that there is an east bound train standing on the right hand track of the passing siding at the west end of the single track section 0 shown in the drawing, and that the dispatcher located at the distant tower DT desires to have this train proceed in an easterly direction. In order to set up east bound traflfic in the single track section 0 the dispatcher moves the lever L to the right as a result of which the control relay ZW is energized by direct current from the battery I52 through the following circuit-beginning at the battery I52, lever L, winding of the indicating relay 213, primary winding of the transformer E56, line wire I51, secondary winding of the transformer I56, front contact I6I of the detector track relay EDT, winding of the control relay ZW, through the inductance I62, to the common return wire C connected to the neutral point of the battery 52. The current flow so produced is of such polarity that the control relay ZW will be energized toward the right. The control relay ZE will in turn be energized through the following circuit:- beginning at the battery ISd, which has its neutral point connected to the common return wire C, through the polar contact 565 of the relay ZW in its right hand position, through the neutral contact I65 of this same relay, primary winding of the transformer IE8, front contact l6? of the detector track relay EDT, winding of the control relay ZE to the common return wire C. In other words, if the lever L is moved to the right it will supply current to energize the control relay ZW toward the right, which relay in turn will energize the control relay ZE toward the right. The energization of the control relay ZW toward the right will cause clearing of the starting signal 2 through the medium of the home relay iii in a manner as described in the parent application, and the energization of the control relay ZE toward the right will permit clearing of the home relay 8H in a manner as described in the parent application.

With the control relays ZW and ZE energized toward the right the signal 2 is cleared in accordance with traffic conditions ahead and the signal 8 is permitted to clear as soon as the switch points of switch 8S have been locked and providing trafiic conditions in advance are clear.

It should be noted that the application ofcurrent to the control relay ZW by the lever L also caused energization of the line or indication relay 21R and that its back contact I is retracted so that the indicating lamp HE is not energized even though the contact I59 in its energizing circuit is closed.

Let us now assume that the train in question starts in an easterly direction in response to clearing of the signal 2, the entrance of this train on the detector track circuit containing track relay 2DT causes contacts i6! and I18 of this relay 2DT to assume the retracted position, thereby causing a stick circuit for the control relay ZW to be completed which may be traced as followsz-beginning at the right hand side of the battery I64, polar contact 1 ii of the control relay ZW, neutral contact 512 of this same relay, contact I10 of the detector track relay 2DT in its de-energized position, winding of the control relay ZW, inductive reactances I52, to the com mon return wire C connected to the mid-point of the battery 164. The-polarity of the battery I64 with respect to the polarity of the battery I52 is such that the relay ZW will be energized by current flowing in the same direction through the circuit just traced as it was by the battery i512 from the tower previously. In other words, even though the line circuit I51 has been broken at contact I 6i this breaking of the line circuit did not de-energize control relay ZW nor the control relay ZE, the control circuit of this latter relay including contacts I and I66 of the control relay ZW.

Let us now see what effect the dropping of the detector track relay 2DT will have upon the indicating lights or signals in the tower DT. With 10 the line circuit I51 broken at the contact I6I of the track relay ZDT, as far as the flow of direct current is concerned, the condenser I15 not permitting the flow of direct current, the indication relay HR in the tower DT is de-energized 15 thereby closing energizing circuit for the indicating lamp ZIE (and momentarily sounding a bell if such is used) which includes the back contact I55 of the indicating relay 21R and the contact I 50 controlled by the lever L. The dispatcher in 20 the tower is therefore informed that a train has accepted the signal 2 and is moving into the single track section 0 by the indication received through the indicating lamp 21311. As soon as the train passes ofi of the detector track circuit including 25 relay ZDT the indication lamp 21E in the tower DT is again extinguished for obvious reasons.

Let us now assume that the train proceeds through the single track section 0 in an easterly direction and treads upon the detector track circuit including the detector track relay 1DT thus effecting de-energization of this track relay and dropping of the contact I61 thereof. The dropping of contact I61 de-energizes the control relay ZE, but it should be noted that no harm is done because neither the signal 8 nor the signal 7 can be clear at any time while the detector track relay 'iDT is de-energized so that there is no need of the control relay ZE being energized. With the contact I61 in its de-en- 40 ergized position the following circuit having alternating current flowing therein is completed for energizing the primary winding of the transformer I6B:--beginning at the secondary winding of the transformer I69, the primary wind- 45 ing of which is connected to a suitable source of alternating current A. 0., resistance I13, back contact I61 of thedetector track relay 1DT, pri mary winding of transformer I60, front contact 566 of the control relay ZW, polar contact I65 ($0v of this, same relay through the right hand portion of the battery I84 to the common return wire 0 connected to the other side of the secondary winding of transformer 569. This circuit will have a certain amount of direct current fiow- 55 ing therein limited by the resistance I13, but this is deemed immaterial if the transformers I59 and Itt are properly constructed. If desired the resistance H3 may be replaced by a unit consisting of an inductance and a condenser in se- 60 ries tuned to the frequency of the source AC. This circuit will also have alternating current flowing therein which will induce an alternating current voltage in the secondary winding of the transformer IE8 which in turn will cause alter- 65 nating current to flow in the line circuit including line wire 551 as followsz-beginning at the secondary winding of the transformer I60, the line wire E51, the primary winding of a transformer I56 the winding of the indication relay 70,- 2IR, the lever L, through the right hand portion of the battery I52, to the common return wire C, through the condenser I18, through the inductive reactances 519, front contact IBI oi the detector track relay 2DT, back to the second- 75,

through the tuned unit I18I19.

ary winding of the transformer I60. The condenser I18 and the inductive reactances I19 have such constants as to constitute a tuned unit resonated to the frequency of the alternating current supply A. C., that their inclusion in the circuit will not materially interfere with the flow of alternating current but will prevent the flow of direct current through that portion of the circuit. In this connection it should be noted that the inductive reactances I62 in series with the winding of the control relay ZW are in multiple with the tuned unit comprising devices I18 and I19. 'The impedance to the flow of alternating current through the relay ZW together with that of the inductive reactances I62 is so high that alternating current will prefer to take the path The flow of alternating current in the circuit just traced will effect energization of the line or indicating relay 1IR thereby causing its front contact I86 to assume its raised position and thereby completing a circuit for the indicating lamp HE, (and momentarily sound a bell if such is used) which circuit includes this contact I88 and the contact I5I of the lever L. The dispatcher will therefore be informed of the presence of the train on the detector track circuit including track relay 'ID'I by the illumination of the indication lamp 11E. It may be stated here that the source A. C. may consist of an alternating current transmission line, a generator, or a suitable tuned or constantly driven interrupter.

We have now considered how the control relays ZW and ZE may be controlled from the tower DT, and how an indication may be received as to the occupancy of either the detector track circuit including the relay EDT or the detector track circuit including the relay EDT, separately. Let us now consider the simultaneous occupancy of both of these detector track circuits, that is, let us assume that both the detector track relay 2DT and the detector track relay IDT are de-energized when the lever L is in the right hand position. With the lever L in the right hand position the indication relay 21B is of course energized, and all of the indicating lamps at the tower are deenergized. Let us now assume that the detector track relays EDT and 'IDT both assume the de-energized position due to the presence of trains. With the detector track relay ZDT deenergized the control relay ZW will be energized by a stick circuit heretofore traced and dropping of the contact I6! of the track relay ZDT will open the line circuit including wire I51 as far as the flow of direct current is concerned, because direct current cannot flow through the condenser I15. Therefore, the indicating relay 2113. in the tower is de-energized and the indicating lamp 211] is energized through a circuit including the contact I55 of this relay HE and the contact I50 of the lever L also. The deenergizing of the track relay 'IDT will cause alternating current to be applied to the primary winding of the transformer I60, and this alternating current will induce a voltage in the secondary winding of transformer I80, which voltage causes alternating current to how in the following circuit:- beginning at the secondary winding of the transformer IEO, line wire I51, primary winding of the transformer I55, the winding of the indicating relay 21R through the right hand portion of the battery I52, through the common return wire C, through the tuned unit comprising the condenser I15 and the inductive reactances Ila,

back contact IBI of the track relay 2DT, back to the secondary winding of transformer I60. The flow of alternating current in the circuit just traced will cause the indication relay HR to attract its front contact I80, thereby (momentar- 5 ily sounding a bell if such is used) energizing the indicating lamp 'IIE through this contact I80 and the contact I5I of the lever L. In this connection it is desired to point out that inductive reactances I14 and the condenser I15 consti- 10 tute a resonated unit tuned to the irequency of the alternating current source A. C., so that the presence of this tuned unit I14-I15 in the circuit just traced does not materially restrict the flow of such alternating current. It is thus ap- 15 parent that the arrangement shown in the drawing permits the simultaneous and continuous indication of the presence or absence of trains at two different points on the railroad over the same control wire or circuit, and that a system has been shown in which only one line wire per single track section is required for setting up the direction of trafiic that may move in such single track section and for indicating at entrance or departure of trains to or from both ends of this single track section simultaneously.

Having thus shown and described one specific embodiment of the present invention it is desired to be understood that the particular arrangement shown and described has been illustrated for the purpose of conveying the underlying purpose of the present invention and the manner in which it may be applied to the particular type of single track absolute-permissive-block signal system shown, and that no attempt has been made to illustrate how the invention may be applied to other systems, and further that the particular embodiment of the invention illustrated has not been selected to show the preferred construction preferably employed in practicing the invention nor that the arrangement shown has been selected to show the scope or the invention, and that various changes, modifications and additions may be made to adapt the invention to other systems of single track or double track railway signalling and that certain features may be omitted if desired all without departing from the scope of the invention or the idea of means underlying the same except as demanded by the scope of the following claims.

What we claim as new is:--

1. In a train dispatching system, the combination with a single track railway having a passing siding, signals associated with said siding and governing the movement of trains into and out of said siding, a relay controlled over a line circuit from a distant point for causing one of said signals to indicate proceed in response to the energization of said control relay by a direct current, two detector track circuits, and means for indieating at the tower when one of said detector track circuits is occupied including means for opening the circuit so far as the flow of direct current is concerned, and means for indicating the condition of occupancy of the other detector track circuit over said line wire responsive to the flow of alternating current.

2. In a train dispatching system, the combination with a single track section joining two passing sidings, signals at the ends of said single track section governing the entrance and departure of trains into and from said section, a polar relay for controlling said signals and controlled in response to direct current flowing over a single line circuit from a dlspatchers tower located at a distant point in accordance with the polarity of the direct current applied to said line circuit by the train dispatcher, a detector track circuit located at each end of said single track section, means for indicating when one of said detector track circuits is occupied responsive to the opening of said line circuit so far as the flow of direct current is concerned, and means for indicating the occupancy of the other detector track circuit responsive to the flow of alternating current applied to said line circuit when said another detector track circuit is occupied.

3. Control and indication means for distant signals and track circuits associated therewith comprising, two distant signals separated by a considerable distance, a control relay at one of said signals for controlling the same and controlled from a dispatchers office, a control relay at the other signal for controlling the same and controlled by the first mentioned control relay, and a transformer forinductively coupling the energizing circuits for said control relays for the purpose of transmitting alternating current from one into the other of said circuits.

4. Control and indication apparatus for train dispatching systems comprising, a distant signal, a line circuit connecting a dispatchers office and said signal for controlling said signal subject to traflic conditions in advance thereof and in accordance with the wishes of a dispatcher at said oifice, a relay responsive only to the flow of direct current connected in series in said line circuit, another relay only responsive to the flow of alternating current connected in series with said first mentioned relay, two separate indicating devices at said ofiice controlled by said relays, an automatic means for controlling the energization of said line circuit in accordance with conditions at the location of said signal, whereby said signal may be controlled from said dispatchers oflice and two distinct and concurring indications may be received at said dispatchers ofiice over the same line wire.

5. In a train dispatching system, the combination with a distant signal, a track circuit associated with said signal for controlling the signal in such a way that said signal indicates stop if said track circuit is occupied, a train dispatchers office, a line circuit connecting said ofiice and said signal for controlling said signal subject to traific conditions, a relay responsive only to direct current and included in said line circuit and located at said dispatchers office, a relay responsive only to alternating current and included in said line circuit at said dispatchers ofiice, a contact included in said line circuit which is open when said track circuit is occupied, a direct current source connected in said line circuit, means for closing said line circuit at said dispatchers ofiice which circuit if closed will permit said signal to clear if trafiic conditions are clear and said track circuit is unoccupied, whereby it said track circuit is occupied said first mentioned relay is de-energized, and means responsive to other traffic conditions for applying alternating current to said line circuit to effect energization of said alternating current line relay.

6. In combination, a railway signal, a polarized relay for controlling said signal, a track circuit adjacent said signal and including a track relay, a normal anda reverse pick-up circuit for energizing said polarized relay, and a stick circuit for said polarized relay including one of its own polar contacts and a back contact of said track relay for retaining said polarized relay in an energized condition as long as said track relay remains deenergized.

- 7. In combination, a railway trafiic controlling device, a polarized relay for controlling said traffic controlling device, a track circuit adjacent said 5 trafiic controlling device and including a track relay, anormal and areverse pick-up circuit for energizing said polarized relay, and a stick circuit for said polarized relay including one of its own V polar contacts and a back contact of said track 10 relay for retaining said polarized relay in an energized condition as long as said track relay remains deenergized.

8. In combination, a local control oflice, a traffic controlling device at a distant point, a polarized 15 control relay for controlling said trafiic controlling device and located near said trafiic controlling device, a line circuit connecting said office and distant point and including the winding of said polarized relay, a track circuit adjacent said trafllc 20" controlling device including a track relay, a front contact of said track relay included in said line circuit, means at said office for energizing said line circuit by current of one polarity or the other to w control said traific controlling device, indicating no means in said line circuit at said ofiice to indicate the continuity of said line circuit and the open condition of said front contact, and a stick circuit for said polarized relay including one of its :3"; own polar contacts and a back contact of said track relay for retaining said polarized relay in an energized condition as long as said track relay remains deenergized.

9. In a traffic controlling system, the combination with a distant traific controlling device, of a local central ofiice, a source of direct current at said ofiice, a circuit connecting said office and said distant traiiic controlling device for controlling said device through the medium of said source, a relay at said ofiice included in said circuit, means do for opening said circuit at said trafiic controlling device under certain trafiic conditions thereby effecting deenergization of said relay to indicate such traffic conditions, and means for indicating at said office other traflic conditions by super- 45 imposing at said trafiic controlling device alternating current on said circuit.

10. In a trafiic controlling system, the combination with a distant trafiic controlling device, of a local central ofiice, a source of direct current at 50 said ofiice, a circuit connecting said oflice and said distant tramc controlling device for controlling said device through the medium of said source, means at said traffio controlling device for controlling said circuit under certain trafllc condi- 55 tions to indicate such traffic conditions, and means for indicating at said oflice other trafiic conditions by superimposing at said traflic controlling device alternating current on said circuit. 60

11. In combination, a local control ofiice, a traffic controlling device at a distant point, a polarized control relay for controlling said traflic controlling device and located near said trafiic controlling device, a line circuit connecting said oflfice and dis- 55 tant point and including the winding of said polarized relay, a track circuit adjacent said traffic controlling device including a track relay, a front contact of said track relay included in said line circuit, means at said office for energizing 70 said line circuit by current of one polarity or the other to control said traffic controlling device, indicating means in said line circuit at said ofilce to indicate the continuity of said line circuit and the open condition of said front contact, other indicat- 75 ing means at said ofiice controlled by alternating current flowing in said line circuit, and a stick circuit for said polarized relay including one of its own polar contacts and a back contact of said track relay for retaining said polarized relay in an energized condition as long as said track relay remains deenergized.

12. In a traffic controlling system, the combination with a distant trafiio controlling device, of a local central oilice, a source of direct current at said office, a circuit connecting said office and said distant traflic controlling device for controlling said device through the medium of said source, and means for indicating at said central oifice the conditions of traftic at a distant point by applying alternating current to said circuit at such distant point.

13. In a traflic controlling system, the combination with a distant traflic controlling device, of a local central oifice, a source of direct current at said office, a circuit connecting said office and said distant trafiic controlling device for controlling saidv device through the medium of said source, and means controlled by a track circuit for indicating at said central office the conditions of trafi'ic at a distant point by applying alternating current to said circuit atsuch distant point.

14. In a railway signal system; a. plurality of circuits arranged end-to-end and individually controlling railway trafiic controlling devices; a relay, a source of current and circuit controlling means. included in each of said circuits; and cooperating means in each circuit for coordinating said circuits to permit the transmission of current from a different source over said circuits the full distance over which said circuits extend endto-end.

15. In a railway signal system; a plurality of circuits arranged end-to-end and individually controlling railway trafiic controlling devices; a relay, a source of direct current and circuit controlling means included in each of said circuits; and cooperating means in each circuit for coordinating said circuits to permit the transmission of. alternating current over said circuits the full distance over which said circuits extend end-toend.

16. In a trafiic controlling system, the combination with a distant trafic controlling device, of a local central office, a source of direct .5

current at said office, a circuit connecting said office and said distant traific controlling device for controlling said device through the medium of said source, and means for transmitting two distinctive indications to said central ofiice over said lo,

dium of alternating current. 15 17. In a trafiic controlling system, the combination with a distant trafiic controlling device, of a local central oiiice, a source of direct current at said ofiice, a circuit connecting said oilice and said distant trafiic controlling device for con- 20 trolling said device through the medium of said source, and means for transmitting two distinctive indications to said central office over said circuit one of which is transmitted only under certain trafiic conditions and by opening said circuit to the flow of current of one character and ascertaining its continuity and the other of which is transmitted through the medium of alternating current.

18. In a railway signal system; a plurality of circuits arranged end-to-end and individually controlling railway traffic controlling devices; a relay, a source of direct current and circuit controlling means included in each of said circuits; means for inductively coupling said circuits to 235 permit the transmission of alternating current over said circuits the full distance over which said circuits extend end-to-end, and means for applying alternating current to one end of said end-to-end circuits and detecting such alternating current at the other end of said end-to-end circuit through the medium of said circuits and said means for inductively coupling.

NEIL D. PRESTON. OSCAR H. DICKE. 

